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     Ants are small individuals but are great in groups. Ants first attracted theof software engineers in the early 1990s. A single ant cannot do much on its own, but a group of ants as a whole candifficult problems. That interested people like Marco Dorigo, who is one of the founders of a field knowngroup intelligence.
     Ants are good atthe shortest possible route between a food source (来源)and their nest. This reminds us of a classic computational (计算的) travelling-salesman problem. Given a list of cities and their location apart, the salesman must find theroute needed to visit each city once. As the number of citiesthe problem gets much more.
     Ants solve their own problem by using chemical signals called pheromones (信息素). When an antfood, she takes it back to the nest, leaving behind a pheromone trail that will attract others. The more ants that follow the trail, theit becomes. However,the pheromones evaporate (挥发) ,so once all the food has been collected, the trail soon goes cold. This rapid evaporation means long trails are less important than short ones, all else being equal. Pheromones thus turn theintelligence of the individual ants into something more powerful.